1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine of the type having a high pressure fuel pump and a fuel injection valve for each engine cylinder.
2. Description of the Prior Art
One fuel injection systems known from European Patent Disclosure EP 0 987 431 A2, has one high-pressure fuel pump and one fuel injection valve communicating with it for each cylinder of the engine. The high-pressure fuel pump has a pump piston, which is driven by the engine in a reciprocating motion and defines a pump work chamber. The fuel injection valve has a pressure chamber communicating with the pump work chamber and also has an injection valve member, by which at least one injection opening is controlled and which is movable, acted upon by the pressure prevailing in the pressure chamber, in the opening direction counter to a closing force to uncover the at least one injection opening. A first electrically actuated control valve is provided, by which a connection of the pump work chamber with a relief chamber is controlled. A second electrically actuated control valve is also provided, by which a connection of a control pressure chamber with a relief chamber is controlled. The control pressure chamber communicates with the pump work chamber via a throttle restriction. The control pressure chamber is defined by a control piston, which is braced on the injection valve member in its closing direction and which is urged in the closing direction of the injection valve member by the pressure prevailing in the control pressure chamber. For a fuel injection, the first control valve is closed and the second control valve is opened, so that high pressure cannot build up in the control pressure chamber, and the fuel injection valve can open. However, when the second control valve is opened, fuel flows out of the pump work chamber via the control pressure chamber, so that of the fuel quantity pumped by the pump piston, the fuel quantity available for injection is reduced, as is the pressure available for the injection. As a consequence, the efficiency of the fuel injection system is not optimal, and the course of the fuel injection cannot be adjusted in the desired way.